1. Technical Field
Apparatus consistent with exemplary embodiments broadly relates to techniques for generating collinear and phase-locked replicas of an electromagnetic radiation pulse.
2. Description of Related Art
An important application that calls for a pair of phase-locked pulses is the so called Two-dimensional (2D) optical spectroscopy. This technique is used by a growing community of physicists, chemists and biologists both in the infrared (IR) range, targeting vibrational transitions (2DIR spectroscopy), and in the visible range, targeting electronic transitions (2D electronic spectroscopy). In its most simple implementation, 2D spectroscopy uses a pump-probe geometry with two phase-locked collinear pulses exciting the sample, which is then probed by a third non-collinear pulse.
A second application concerns the FTIR (Fourier Transform infrared) spectrometry. In this technique two delayed broadband beams impinge on a sample in order to measure its absorption spectrum.
The generation of phase-locked delayed pulse replicas is currently performed by means of two main techniques. The first technique is based on the Michelson interferometer according to which an interference pattern is produced by splitting a beam of light into two paths, bouncing the beams back and recombining them. This technique requires complex feedback circuits to keep the interferometer in stability conditions. Moreover, higher feedback accuracy is required for shorter wavelengths; therefore, it is observed that the Michelson interferometer method does not appear satisfying for generating pulse replicas of radiation with sub-wavelength accuracy.
The generation of delayed pulse replicas by means of a Michelson interferometer is described as an example in M. U. Wehner et al., Opt. Lett. 22, pages 1455-1457 (1997).
The second known technique is based on a “pulse shaper” which generates the pulse replicas by suitably applying spectral amplitude modulation and spectral phase modulation to a pulse. This technique appears particularly complex and expensive.
Document US-2009-0161092 describes an optical device employed to generate delayed pulse replicas to be employed in a multidimensional spectrometer.
In optics, the Babinet-Soleil compensator is known. The Babinet-Soleil compensator is a continuously variable, zero-order retarder employing a birefringent wedge which is movable and another birefringent wedge which is fixed to a compensator plate. The orientation of the long axis of the wedges is perpendicular to the long axis of the compensator plate. The known Babinet-Soleil compensators are employed in optics to introduce phase delays between two orthogonal polarizations of an electromagnetic field; such phase delays are limited to one optical cycle (e.g. a maximum phase delay of 5.5 fs at 1650 nm) and their effect is to rotate the polarization or act as phase equalizers. Movement of the birefringent wedge is required in order to tune the device to the given electromagnetic field frequency.